What Is a Compound Sentence? Definition and 33 Examples

It rained all night, so the match was cancelled. That's a compound sentence: two complete sentences combined into one. Each half has its own subject and verb and would make sense alone, and a comma plus so holds them together.

It is a worthwhile exercise to learn how to join sentences like this. Writing Next, a 2007 review of writing research done for the Carnegie Corporation, found that sentence combining lessons had an average effect size of 0.50 for students in grades 4 to 12. How much a method helps is usually quantified by an effect size, and most of those studies compared sentence combining with traditional grammar lessons. The authors termed the results "consistently positive and moderate in strength."

This guide covers the rules, a quick test and the most common mistakes. Here for the examples only? Skip to the 33 examples.

The short version

• It has two or more independent clauses, and each could stand alone as a sentence.
• Join the clauses with a comma plus and, but, or, so, yet, for or nor, or with a semicolon.
• Words such as however and therefore need a semicolon before them and a comma after them.
• One subject with two verbs (Sam locked the door and left) is not compound, so it takes no comma.

What is a compound sentence?

So what actually counts as one? Purdue University's Online Writing Lab (Purdue OWL) gives the standard compound sentence definition: a sentence made of at least two independent clauses. An independent clause is a group of words with a subject, a verb and a complete thought, the kind of thing you could put a full stop after.

You've probably written hundreds of these without noticing. The kettle boiled and Sam poured the tea are two simple sentences, and each has one subject and one verb. With a comma and the word and in the middle, they turn into The kettle boiled, and Sam poured the tea.

That's what sets compound apart from complex. A complex sentence has a dependent clause, one that can't stand alone (because the kettle boiled). A compound one consists of only clauses that can.

Compound sentence structure: the formula

There are three ways to put one together, and every clause in the formulas below is an independent clause.

Nothing stops you at two clauses, by the way: I washed, Priya dried, and Tom put the plates away joins three of them.

The 7 coordinating conjunctions (FANBOYS)

Coordinating conjunctions are the seven words that can join two independent clauses with a comma. Purdue OWL lists the same seven. Teachers often remember them as FANBOYS, with one letter for each word in the table below.

Two words need care. For sounds formal, so most people use because instead, which makes the sentence complex. Nor follows a negative clause, and the Cambridge Dictionary notes that the helping verb comes before the subject after it. That's why we write nor did she text rather than nor she texted.

Comma and semicolon rules

Getting the punctuation right mostly comes down to five rules. None of them is tricky once you've seen it in action.

Put a comma before the conjunction

First things first: the comma comes before the conjunction, not after it. According to Purdue OWL, "a comma is needed before the coordinating conjunction." Picture The bus was late, so I walked. The pause lands right where your voice would drop.

You can skip the comma when both clauses are short

Very short clauses can get away without one. The University of Wisconsin Writing Center allows this exception, and Hamilton College says the same: "You may omit the comma if the two clauses are short and closely related." I knocked but nobody answered reads perfectly well. If you're torn, though, put the comma in. It's never wrong there.

Use a semicolon when there is no conjunction

What if there's no and or but at all? Then you want a semicolon. Here's how Purdue OWL words it: "Use a semicolon when you link two independent clauses with no connecting words." Only do this when the two halves really are about the same thing. The library was silent; everyone was revising works because the second half explains the first.

Use a semicolon and a comma with however and therefore

Now for however and therefore. They seem to do the same job as but or so. They're actually transition words, though, so the punctuation is different. Purdue OWL's rule is a semicolon before the word, and Hamilton College adds that a comma usually comes after. So it's It was late; however, the shop was still open, with punctuation on both sides of however.

Do not put a comma between two verbs

This last rule is easy to miss. Look at Sam locked the door and turned off the lights. Sam does both things. Here and joins two verbs rather than two clauses. That's called a compound predicate, and there's no comma before the and. The University of Wisconsin says so plainly: "Commas are not used between two verbs, two subjects, two complements, or two objects."

33 compound sentence examples

Every one of these has two independent clauses. The word doing the joining is in bold.

Joined with and

Use and when the second clause simply adds something.

1. The kettle boiled, and Sam poured the tea.

2. Our flight landed twenty minutes early, and for once the taxi queue was short.

3. Nadia got the printer working again, and Ben ran off copies for everyone.

4. The rain finally stopped, and half the town seemed to head for the park.

5. I tackled the kitchen on Saturday, and my brother did the big supermarket shop.

Joined with but

But sets up a contrast between the two halves.

6. The shop was open, but there was hardly anything left on the shelves.

7. Leo revised for weeks, but the exam still threw him.

8. Everyone raved about the film, but we nearly fell asleep halfway through.

9. She meant to ring her gran, but her phone had died again.

Joined with or

Or offers a choice, or warns you what happens otherwise.

10. We can get the train, or Dad can run us to the airport.

11. You'll need to water the tomatoes today, or the leaves will start curling.

12. The meeting could move to Friday, or we could just do it online.

Joined with so

So shows a result. The cause comes first.

13. The road was flooded, so we had to go the long way round.

14. My alarm never went off, so I missed the whole first lesson.

15. Every table in the café was taken, so we ended up eating our sandwiches on a bench.

16. Prices went up in March, so the club had to raise its fees.

Joined with yet

Yet works like but, with a bit more surprise in it.

17. The test was only twenty questions long, yet loads of us ran out of time.

18. He trained every day for months, yet his times barely moved.

19. The house looked tiny from the street, yet somehow it had four bedrooms.

Joined with for

For means because. It sounds old-fashioned, so you'll mostly see it in formal writing.

20. We packed extra blankets, for the forecast said snow was on the way.

21. Nobody in the village slept that night, for the river was still rising.

Joined with nor

Nor only follows a negative, and the helping verb comes before the subject.

22. Mia did not answer the door, nor did she reply to my text.

23. The report doesn't explain the delay, nor does it give us a new date.

Joined with a semicolon

No conjunction here. The semicolon does the job on its own.

24. The library was silent; everyone was revising for exams.

25. My sister loves horror films; I can't even watch the trailers.

26. The first draft took me a whole week; the second one took an afternoon.

27. We scored in the third minute; the other team never got going after that.

Joined with a semicolon and a transition word

The transition word sits after the semicolon, with a comma straight after it.

28. The trains were cancelled; however, the buses were still running.

29. Ali saved a bit every month; therefore, he could pay for the trip himself.

30. The paint was still wet; as a result, we moved the party outside.

31. The recipe looked simple enough; in fact, it took me three hours.

32. Jess forgot half her lines; nevertheless, the audience loved it.

33. We booked our seats early; otherwise, we'd have been standing at the back.

Is it compound? A 3-question test

Stuck on a sentence? Ask yourself three things.

1. Are there two subjects, each with its own verb? In The phone rang, and Dad answered it, the phone does the ringing and Dad does the answering.
2. Could each part stand alone as a sentence? Split it and see: The phone rang. Dad answered it. Each one works as a sentence, so you've got two independent clauses.
3. Is the join correct? You need one of three joins: a comma with a FANBOYS word, a semicolon, or a semicolon with a transition word. A comma by itself won't do. That's a comma splice, which we come back to below.

If you get three yeses, it's compound. Watch out for these, though. They look compound, but they aren't:

• Sam and I went shopping. Simple. Sam and I is a compound subject, meaning two people doing one thing.
• Lena opened the window and let the cat out. Simple. There's one subject (Lena) with two verbs.
• She left early so that she could catch the train. Complex. So that she could catch the train can't stand on its own.

Simple vs compound vs complex vs compound-complex sentences

Every sentence falls into one of four types. It all depends on which clauses it has, and how many.

Look at the bus sentences in the table. What makes one compound and the other complex is the joining word. So keeps the two clauses equal. Because doesn't: I walked can stand alone, but because the bus was late can't. Although, when and if behave the same way as because, so they make a sentence complex too. Our guide to the complex sentence covers those words, and where the comma goes with them.

How to write a compound sentence in 3 steps

1. Start with two related simple sentences. Something like The library closes at six and We still have an hour to study.
2. Choose a joiner that matches the link. And adds an idea, but and yet set up a contrast, or gives a choice and so shows a result.
3. Punctuate the join. A comma goes before the conjunction. If you'd rather skip the conjunction, use a semicolon on its own.

This kind of practice has research behind it. The IES practice guide on teaching elementary students to write recommends teaching children to "construct sentences for fluency, meaning, and style." It rates the evidence for that as moderate. To be fair, that same recommendation also takes in handwriting, spelling and typing, so the rating isn't for sentence work alone.

Stuck on how to join a pair? A free sentence rewriter can suggest a version. We tried TotBot's Sentence Rewriter on the pair The library closes at six. We still have an hour to study. We set it to the Formal tone and one variant. Here's what came back:

The library closes at six, so we still have an hour to study.

That's right. So shows the result, and the comma comes just before it.

4 compound sentence mistakes and how to fix them

These four mistakes show up everywhere, from school essays to work emails. Our guide to common writing mistakes has a longer list if you want one.

1. Joining two clauses with only a comma

The road was icy, the school opened late is a comma splice. A comma just isn't strong enough to hold two independent clauses together on its own. There's more on this in our guide to run-on sentences and comma splices.

The fix: Add a conjunction (The road was icy, so the school opened late), swap the comma for a semicolon (The road was icy; the school opened late) or split it into two sentences.

2. Putting a comma before the second verb

In Sam locked the door, and turned off the lights, Sam is the only subject. Sam's doing two things, so that comma has no business being there.

The fix: Take the comma out, or give the second half its own subject: Sam locked the door, and he turned off the lights.

3. Using however with only a comma

It was raining, however we went for a walk is a comma splice too. However might feel like a conjunction, but it isn't one.

The fix: Put a semicolon before however and a comma after it: It was raining; however, we went for a walk.

4. Chaining too many clauses with and

Technically this is compound. It's also exhausting to read, because there's nowhere to take a breath:

We missed the bus and it started to rain and my phone died and we had to walk home in the dark.

We ran that exact sentence through TotBot's sentence simplifier to see what it would do. Its first version was:

We missed the bus, it started to rain, my phone died, and we had to walk home in the dark.

Two of the three ands are gone, which helps. It's still one long sentence, though, so you might want to break it up yourself.

The fix: Keep it to one or two clauses per sentence: We missed the bus. It started to rain, and my phone died. We had to walk home in the dark.

Practice: join these simple sentences

Your turn. For each pair, pick a joiner that fits the meaning and make one sentence.

1. The bus was late again. / I ended up walking to school.
2. Maria drinks tea all day. / Her husband can't start the morning without coffee.
3. We could cook tonight. / We could just order a pizza.
4. The museum was shut for repairs. / We spent the afternoon in the park instead.

Run out of pairs? A sentence generator will write short sentences on whatever topic you pick. Join them up two at a time.

Quick quiz: compound or not?

Label each one compound, simple, complex, compound-complex or comma splice. Watch for traps.

1. The phone rang, and Dad answered it.
2. Sam and I went shopping.
3. Lena opened the window and let the cat out.
4. I stayed home because I had a cold.
5. The bakery was closed; we bought bread at the supermarket.
6. The sun was hot, we stayed in the shade.
7. The train was late; therefore, we missed the start of the show.
8. When the bell rang, the students packed up, and the teacher wiped the board.

FAQs

How many independent clauses does a compound sentence have?

At least two, and there's no rule about the maximum. I cooked, Sam washed up, and Priya made the tea has three, and it reads fine. Go much past that, though, and you'll probably lose your reader halfway through.

Does a compound sentence always need a comma?

Most of the time. It goes right before the joining word, as in It rained, so we stayed in. There are two exceptions. Very short pairs, like I knocked but nobody answered, can do without it. And a semicolon doesn't need a comma after it, unless the next word is something like however.

Can you use a semicolon instead of a conjunction?

You can. The two ideas just have to belong together. The shop was shut; we went home works. But The shop was shut; my cousin likes jazz? Your reader will wonder what jazz has to do with anything.

Does a compound sentence have a dependent clause?

No. Add one and it isn't compound any more. Say you start with It rained, so we stayed in and add When the match ended to the front. That's now compound-complex. With only one independent clause next to it, you'd have a complex sentence instead.

Compound vs complex sentence: what is the difference?

The question is whether both parts could stand alone. Split I was tired, so I went to bed and you get I was tired and I went to bed. Both work as sentences, so it's compound. Now try I went to bed because I was tired. You can't say Because I was tired on its own and call it a sentence. That makes it complex.

Is "Sam and I went shopping" a compound sentence?

No, although it looks like it could be. Sam and I is a compound subject, which just means two people share the one verb, went. There's still only one clause, so it's a simple sentence. Make it Sam went shopping, and I stayed home and now it's compound.

Wrapping up

So, to sum up. When both halves of a sentence could stand alone, they need a proper join. You've got three to pick from: a comma plus a FANBOYS word, a semicolon by itself, or a semicolon with a word like however after it. And if one part can't stand alone, you're not looking at a compound sentence at all.

From here, it's mostly practice. A sentence generator will give you short sentences to join up, and the sentence rewriter shows you other ways to word a line you've written. Got a sentence that's run away with you? Try a sentence simplifier. Whatever these tools suggest, check it against the rules above before you use it.

Cheat sheet: punctuation for joining clauses

Examples written by the TotBot team. Tool results are shown exactly as the tools produced them.

Sources: Purdue OWL, Punctuation in Sentences; Purdue OWL, Identifying Independent and Dependent Clauses; Purdue OWL, Commas vs. Semicolons; University of Wisconsin-Madison Writing Center, Coordinating Conjunctions; Hamilton College Writing Center, Punctuation Patterns; Cambridge Dictionary, Nor; Graham and Perin, Writing Next (Carnegie Corporation, 2007); Graham et al., Teaching Elementary School Students to Be Effective Writers (IES, 2012).